The conformations of the DNAs and RNAs have been of great interest because an understanding of how they work follows from a knowledge of their forms. We are determining the detailed molecular conformations of entire nucleic acid molecules using classical potential energy calculations, minimizing the energy as a function of all conformational angles simultaneously. This approach has given good agreement with experimental data for a number of RNA subunits. We propose to extend these calculations to dimeric subunits of DNA in order to examine the effect of the bases on conformation, and to elucidate the conformational differences between the DNAs and RNAs, and between the A and B forms of the DNAs. It is also proposed to calculate conformations for dimeric subunits of RNA which contain rare nucleotides occurring in the loops of tRNAs in order to examine the role that these less common species play. Further calculations are to be made for the various base sequences of trimeric RNA and DNA subunits, to establish the conformational restrictions imposed on these larger units. Finally, conformational calculations are to be made for double stranded subunits, as a basis for future calculations on the interaction of drugs with DNA.